
package org.apache.solr.search;

import org.apache.lucene.search.FieldComparatorSource;
import org.apache.lucene.search.SortField;


/**
 * Extra lucene sorting utilities & convenience methods
 *
 *
 *
 */

public class Sorting {


  /** Returns a {@link SortField} for a string field.
   *  If nullLast and nullFirst are both false, then default lucene string sorting is used where
   *  null strings sort first in an ascending sort, and last in a descending sort.
   *
   * @param fieldName   the name of the field to sort on
   * @param reverse     true for a reverse (desc) sort
   * @param nullLast    true if null should come last, regardless of sort order
   * @param nullFirst   true if null should come first, regardless of sort order
   * @return SortField
   */
    static final FieldComparatorSource nullStringLastComparatorSource = new MissingStringLastComparatorSource(null);

    public static SortField getStringSortField(String fieldName, boolean reverse, boolean nullLast, boolean nullFirst) {

        if (nullLast) {
            if (!reverse) {
                return new SortField(fieldName, nullStringLastComparatorSource);
            }
            else {
                return new SortField(fieldName, SortField.Type.STRING, true);
            }
        }
        else if (nullFirst) {
            if (reverse) {
                return new SortField(fieldName, nullStringLastComparatorSource, true);
            }
            else {
                return new SortField(fieldName, SortField.Type.STRING, false);
            }
        }
        else {
            return new SortField(fieldName, SortField.Type.STRING, reverse);
        }
    }
}
